1. Field of the Invention
This invention pertains in general to a closure with inflatable seals for sealing a nozzle opening into a nuclear steam generating vessel, and more particularly, to a self latching nozzle dam which can be installed quickly without having to align screws or pins between the nozzle dam and nozzle wall or nozzle hold down ring.
2. Description of the Prior Art
Many nozzle dam designs are described in the prior art which have as their objective, quick installation features in order to minimize exposure time to nuclear radiation, which exists in the immediate work environment within the vessel.
For example, U.S. Pat. No. 4,667,701, patented by Evans et al. May 26, 1987, describes a nozzle dam sealing system having a permanent flange ring that is concentric with the circular opening of the nozzle, welded to the inside surface of the steam generator around the opening. Typical of installations presently in use, the ring has threaded holes for fastening a dam in place over the nozzle.
An insert, designed to receive a bayonet fastener, is screwed into each threaded hole.
A collapsible, adjustable, support frame similar to a pantograph, has bayonet pin means hingedly attached to one end of the frame, and bayonet pin means attached to the other end without hinges. The support frame is attached by the hinged bayonet pin means to the ring, and oriented vertically, normal to the nozzle ring.
The dam plate of the system, which retains the inflatable seal, is provided in three sections for assembly on the hingedly mounted support frame. The dam plate is in three sections because it must be passed into the vessel by way of a manway which is smaller than an assembled dam.
After assembly of the dam on the frame, the frame with dam is rotated down on the hinged bayonet means attachment until the pins at the other end of the pantograph frame can be installed in the inserts on the opposite side of the opening.
In order to avoid a source of delay during installation of the nozzle dam, assembly of the dam and frame must be accurate, so that the bayonet means align each with a respective insert when the dam is rotated down onto the ring to find the proper seating.
U.S. Pat. No. 5,007,460, patented Apr. 16, 1991 by Zezza et al., improves on U.S. Pat. No. 4,667,701. The nozzle dam is installed into the nozzle opening before the pantograph beams. This reduces the time required to install the nozzle dam system. Six bayonet pins attached to the ends of the beams provide the attachment to the inserts installed in the flange ring.
In order to be able to install the nozzle dam efficiently within the vessel, measurements of the nozzle must be applied to adjusting the pantograph and dam assembly in advance of the actual installation.
U.S. Pat. No. 4,826,036, patented May 2, 1989 by Lewis et al., describes a system which uses toggle type action clamps located at about six points about the circumference of the dam, each to drive a pin radially from the dam into a pocket in the nozzle to secure the nozzle dam in the nozzle. The movement of the pin towards the pocket is also used to generate hydraulic pressure for the expandable seal by way of a plunger that is press-fit on the pin. The plunger, carried by the advancing pin, presses against a bladder containing the hydraulic fluid.
Orientation of each pin with a corresponding pocket is necessary for successful closure.
U.S. Pat. No. 4,637,588, patented Jan. 20, 1987 by Wilhelm et al. describes a system which avoids need to align a screw or pin on the dam with corresponding receiving means in the nozzle.
This two-stage system has a foldable sealing nozzle dam plate with an anchor assembly below the plate attached to it by a vertical, threaded shaft assembly that passes up through the plate.
The anchor assembly includes a plurality of arms in a tripod arrangement which may be opened from a folded position, to extend radially from the vertical shaft into frictional engagement with the inner surface of the nozzle. The tripod arrangement is designed to increase radial pressure of the arms against the nozzle surface by movement of a linkage arm coupling of the tripod arrangement up the threaded shaft as the shaft is rotated.